Preparation and use of a heterogeneous rhodium catalyst for the hydrogenation of a double bond of an α-β-unsaturated carbonyl compound

ABSTRACT

A process for preparing an Rh-based catalytic system heterogenized on an organic or mineral support, characterized in that: a) a rhodium derivative with a valency state&gt;0 is reduced in an ether or aromatic solvent and in the presence of a compound chosen from the group consisting of lipophilic tertiary amines, lipophilic tertiary amides and lipophilic quaternary ammonium salts, and b) the mixture thus obtained is adsorbed onto a suitable organic or mineral support. Use of the abovementioned catalytic system to hydrogenate a C═C double bond of an α,β-unsaturated carbonyl compound.

The present invention relates to the preparation and use of an Rh-basedheterogeneous catalyst with high catalytic activity, good stability andhigh selectivity for the hydrogenation of a C═C double bond of anα,β-unsaturated carbonyl compound.

In particular, the present invention relates to the hydrogenation of acompound of general formula (I) to give a compound of general formula(II):

in which Ar, A and n have the meanings given below.

The hydrogenation of multifunctional compounds such as, for example,α,β-unsaturated carbonyl compounds also containing an aromatic orheteroaromatic ring has been and continues to be the subject of bothacademic and applied research, with the aim of identifying catalyststhat are highly selective towards a single function, such as, forexample, the C═C double bond, with formation of small amounts ofby-products such as saturated and/or unsaturated alcohols and/orby-products resulting from the partial or total hydrogenation of thearomatic or heteroaromatic nucleus.

In the course of the present description, the expression “small amounts”means an amount ≦2% or, even more preferably, ≦1%.

Specifically, when larger amounts of by-products are formed, it isusually difficult or even impossible to purify the desired finalcompounds without being penalized by significant losses of yield duringthe purification treatment. This is especially the case when productsfor pharmaceutical use are concerned, i.e. which have relatively highpurity requirements (>99.5%).

Patent GB-A-916 119 describes a process for hydrogenating the olefinicdouble bond of α,β-unsaturated aldehydes and ketones. Althoughcinnamaldehyde and benzalacetophenone are mentioned among thehydrogenatable products, the examples refer only to carbonyl compoundslacking an aromatic substituent. According to these examples, thereaction is preferably carried out in the absence of solvent or in thepresence of polar solvents, at atmospheric pressure and at a temperatureof 25° C. Although other heterogeneous rhodium catalysts are envisaged,a commercial catalyst is used, 5% Rh/C.

However, the present inventors have found that by working under theconditions described in GB-A-916 119, either in alcoholic solvents or intoluene, with commercial catalysts such as 5% Rh/C and 5% Rh/Al₂O₃, thesubstrate (I) in which Ar is (6′-methoxy-2′-naphthyl), n=0 and A=methylshows moderately good selectivity (worse when the solvent is polar), buta mediocre conversion (≦50%) even after long reaction times. The presentinventors have moreover found that more advantageous results areobtained by working at relatively higher temperatures and pressures.However, even under these conditions, the production efficiency is stillentirely insufficient.

The reduction of compound (I), in which Ar=phenyl, n=0 and A=H, alkyl orphenyl, has also been described in React. Kinet. Catal. Lett. 26, 447(1984). The said document describes a hydrogenation in methanol, at roomtemperature and low pressure, with a non-commercial 1% Rh/AlPO₄ catalystand with a substrate/Rh ratio (w/w) of between 300 and 500. When A=H, noreduction takes place. In the other cases, the reduction is fast,although it is sensitive to the steric hindrance. The authors state,without, however, providing experimental data, that the selectivity isquite high and that no saturated or unsaturated alcohols are formed. Itshould be noted, however, that the hydrogenation products thus obtainedneed to be purified by crystallization or chromatography on silica. Inaddition, the preparation of the abovementioned catalyst is toocomplicated to be used in an industrial production. Specifically, itinvolves the preparation of the AlPO₄ support, its impregnation with anaqueous rhodium trichloride solution, drying the precatalytic systemthus obtained at 120° C. and reducing the said precatalytic system undera flow of hydrogen at 200° C.

In more recent documents [Synlett, 117 (1997) and J. Mol. Catalysis A,154, 237 (2000)] for the hydrogenation of hindered carbonyl compounds,with tri- or tetrasubstituted C═C double bonds, 5% Rh on charcoal oralumina with a substrate/Rh ratio (w/w)=20 and 10% Pd on charcoal(pyridine co-catalyst) in a substrate/Pd ratio (w/w)=100 are used aspreferred catalysts. The reaction Is carried out in an aromatic solventsince it is stated to be more selective than the polar solventspreviously used, even though the reaction rate may be relatively lower.In the second of the two documents the effect on the selectivity ofvarious parameters such as the nature of the support, the presence ofadditives, the structure of the substrate to be hydrogenated, etc. arealso pointed out.

Thus, the prior art teaches that selective hydrogenation withheterogeneous catalysts requires the study and refinement of manyparameters and that this frequently relates to the development of aspecific catalyst for each substrate to be hydrogenated.

Normally, the higher the required selectivity, the lower the catalyticactivity of the commercially available catalysts. Thus, their productionefficiency is often too low for them to be used on an industrial scale.Since these catalysts also consist of particles of relatively expensive,and also toxic, precious metals distributed over the surface of an inertsupport, parameters that are important for their industrial applicationalso include a) a distribution that is as homogeneous as possible of themetal particles; b) good stability, with little or no release of themetal (to furthermore avoid contamination of the hydrogenation product);c) a substrate/metal ratio (w/w) that is as favourable as possible; d)the possibility of multiple recycling without any loss of catalyticactivity or selectivity; e) little or no sensitivity to the impuritiesthat may be present in the intermediate (l) subjected to hydrogenation,or to other reaction parameters such as, for example, the dryness of thesolvent.

In the course of the present description, the expression “productionefficiency (TOF)” means the ratio: moles of substrate/gram-atoms ofmetal/time, where the time is expressed in hours.

It has also been reported that a number of rhodium-based catalysts maybe used under two-phase or microemulsion conditions. However, theseconditions have not been used on an industrial scale.

J. Mol. Catalysis 34, 229 (1986) described the hydrogenation of a numberof α,β-unsaturated carbonyl compounds (I) in which Ar=phenyl or phenylsubstituted with a chlorine atom or a methyl group, n=0 and A=phenyl orCOOC₂H₅, in the presence of RhCl₃/Aliqua™ 336, in a 1/(1–1.8) ratio, ina water/dichloroethane two-phase system at 30° C. and at atmosphericpressure. For this catalytic system which, after treatment with hydrogenand interaction with the substrate, conserves an Rh—Cl bond, thepresence of water is essential. In addition, this catalytic system hasrelatively low catalytic activity and production efficiency, isrelatively inefficient in aromatic solvents and is extremely sensitiveto the steric effects of the substrate to be hydrogenated. To overcomethe low production efficiency, recycling of said catalyst was envisaged,but no data regarding the kinetics and selectivity of the recycledcatalyst were given. Finally, it should be pointed out that the sameauthors [J. Mol. Catalysis 34, 221 (1986)] have demonstrated that thesame catalytic system, still under mild conditions, is suitable forhydrogenating naphthalene derivatives to give tetralin. Therefore, thissystem cannot be used to selectively hydrogenate a C═C double bond of anα,β-unsaturated carbonyl compound containing a naphthalene ring.

In more recent studies, such as J. Mol. Catalysis 87, 107 (1994) and J.Catalysis 147, 214 (1994), the reduction of disubstituted aromatic ringsor, respectively, of dibenzo-18-crown-6 ethers, is carried out atatmospheric pressure and at room temperature in the presence oftwo-phase catalytic systems based on RhCl₃/trioctylamine ortricaprylmethylammonium, thus confirming that these catalytic systemsare particularly suitable for hydrogenating aromatic substrates andthat, therefore, they cannot be used to selectively hydrogenate a C═Cdouble bond of an α,β-unsaturated carbonyl compound containing anaromatic ring.

In addition to the drawbacks already mentioned, the abovementionedsystems also have the following drawbacks: (a) in order to avoid thepresence of metallic contaminants in the final hydrogenated product, itis necessary to make the colloidal catalytic particles heterogeneous;(b) in order to be able to reuse the catalytic system several times, itis necessary to select a suitable support that does not release themetal. However, the pursuit of these objectives is obstructed by thefact that there is relatively little information regarding thetechniques for immobilizing colloidal metal particles; this isespecially true as regards reproducible techniques. Thus, there is aneed for a fundamental condition for the development and use ofheterogeneous catalysts at the industrial level.

Chemistry Letters 149 (1987) describes the hydrogenation, at atmosphericpressure and room temperature, of olefinic systems in a 1/1water/ethanol mixture in the presence of a catalyst consisting of adispersion of rhodium colloidal particles protected with a copolymer ofmethacrylate and N-vinyl-2-pyrrolidone on a polyacrylamide gelcontaining amine groups. However, this solvent mixture is unsuitable inthe case of lipophilic organic compounds, since these compounds arerelatively insoluble in the said mixture.

Surprisingly, a process that is simple and easy to apply on anindustrial scale has now been found, for preparing an Rh-based catalyticsystem heterogenized on an organic or mineral support, which has highcatalytic activity (substrate/Rh w/w ratio up to values of an order ofmagnitude of 10⁴) and at the same time high selectivity with regard tothe reduction of substrates of general formula (I) to give, in highyield, high chemical purity and high production efficiency, thecorresponding derivatives of general formula (II).

Thus, a first subject of the present invention is a process forpreparing an Rh-based catalytic system heterogenized on an organic ormineral support, characterized in that:

-   a) a rhodium derivative with a valency state>0 is reduced in an    ether or aromatic solvent and in the presence of a compound chosen    from the group consisting of lipophilic tertiary amines, lipophilic    tertiary amides and lipophilic quaternary ammonium salts, and-   b) the mixture thus obtained is adsorbed onto a suitable organic or    mineral support.

Preferably, the abovementioned reduction is carried out with hydrogen orby hydrogen transfer from a suitable hydrogen donor such as, forexample, formic acid and ammonium or alkylammonium salts thereof inwhich the alkyl contains from 1 to 20 carbon atoms.

Advantageously, the said reduction is performed under mild conditions.The pressure is preferably 5 atm (73.45 psi) or less. The temperature ispreferably between 15 and 40° C. Higher pressures and temperatures donot afford any particular advantages.

Preferably, the rhodium derivative with a valency state>0 is a halide.

Typical examples of ether solvents are tetrahydrofuran,1,2-dimethoxyethane, diglyme (CH₃O—CH₂—CH₂—O—CH₂—CH₂—OCH₃) and the like.

Typical examples of aromatic solvents are toluene, mesitylene,isopropylbenzene, cumene and the like.

Preferably, the lipophilic tertiary amine is an amine of formula NTT′T″,in which T, T′ and T″, which may be identical or different, are a linearor branched alkyl containing from 4 to 20 carbon atoms, a cycloalkylcontaining from 5 to 10 carbon atoms or an alkylphenyl in which thealkyl contains from 1 to 20 carbon atoms.

In turn, the lipophilic tertiary amide is preferably an amideX—CO—NX′X″, in which X′ and X″, which may be identical or different, area linear or branched alkyl containing from 4 to 20 carbon atoms, acycloalkyl containing from 5 to 10 carbon atoms or an alkylphenyl inwhich the alkyl contains from 1 to 20 carbon atoms. The nature of X isnot crucial, and may be any group of aliphatic or aromatic nature.Typical examples of X are methyl, hexyl, lauryl, stearyl, phenyl andnaphthyl.

Finally, the lipophilic quaternary ammonium salt is a quaternary salt offormula [NY¹Y²Y³Y⁴]⁺ Z⁻ in which Y¹, Y², Y³ and Y⁴, which may beidentical or different, are a linear or branched alkyl containing from 1to 20 carbon atoms, a cycloalkyl containing from 5 to 10 carbon atoms oran alkylphenyl in which the alkyl contains from 1 to 20 carbon atoms, oncondition that the total number of carbon atoms in the quaternary saltis at least 14; Z⁻ is Br⁻, Cl⁻, OH⁻ or HSO₄ ⁻.

Advantageously, the tertiary amine is trioctylamine (TOA) or ammoniumsalt) and a support, in the chosen solvent.

The heterogeneous catalysts according to the present invention allow theproduction of compounds of general formula (II) with a selectivity ≧98%,a production efficiency (TOF) at least up to 3×10³ h⁻¹ and a use (w/w)of substrate/Rh of up to 10⁴.

Thus, a second subject of the present invention is a process forhydrogenating the C═C double bond in α,β-unsaturated carbonyl compoundsof general formula (I) according to the following reaction scheme:

in which

-   A is hydrogen, linear or branched alkyl containing from 1 to 8    carbon atoms, cycloalkyl containing from 5 to 10 carbon atoms, COOR    or CONRR′ in which R and R′, which may be identical or different,    are hydrogen, linear or branched alkyl containing from 1 to 8 carbon    atoms or cycloalkyl containing from 5 to 10 carbon atoms, or A has    the meanings given below for Ar;-   n is 0, 1 or 2;-   Ar is phenyl, naphthyl or a 5- to 7-membered heteroaryl containing 1    or 2 hetero atoms chosen from O, N and S, in which the said phenyl,    naphthyl and heteroaryl may be substituted with one or more C₁–C₈    alkyl groups or one or more OH, OR, halogen, COOR or CONRR′ groups,    in which R and R′, which may be identical or different, are    hydrogen, benzyl, linear or branched alkyl containing from 1 to 8    carbon atoms or cycloalxyl containing from 5 to 10 carbon atoms,    characterized in that    the said hydrogenation is carried out in the presence of an Rh-based    catalytic system heterogenized on an organic or mineral support,    obtained by (i) reducing a rhodium derivative with a valency state>0    in an ether or aromatic solvent and in the presence of a compound    chosen from the group consisting of lipophilic tertiary amines,    lipophilic tertiary amides and lipophilic quaternary ammonium salts,    and (ii) adsorbing the mixture thus obtained onto a suitable organic    or mineral support.

Reference is made to the above description as regards the preparation ofthe abovementioned catalyst.

Preferably, the said hydrogenation of the C═C double bond of theα,β-unsaturated carbonyl compounds of general formula (I) is carried outat a temperature of between 0° and 100° C. and even more preferablybetween 20° and 80° C.

In turn, the pressure is preferably between 1 (14.69 psi) and 20 atm(293.8 psi).

Advantageously, the said hydrogenation is carried out in the presence ofa solvent of medium or low polarity such as, for example, a linear orbranched aliphatic hydrocarbon containing from 6 to 12 carbon atoms; acyclic hydrocarbon containing from 6 to 10 carbon atoms; an aromatichydrocarbon such as, for example, toluene, xylene, mesitylene,isopropylbenzene or cumene; an aliphatic ester such as, for example,ethyl acetate, isopropyl acetate or butyl acetate; an aliphatic ethersuch as, for example, tetrahydrofuran; or a chlorinated aliphaticsolvent such as, for example, methylene chloride.

The hydrogenation process according to the present invention was foundto be particularly efficient with regard to the hydrogenation of the C═Cdouble bond of the α,β-unsaturated carbonyl compound of general formula(I) in which Ar is (6′-methoxy-2′-naphthyl), n=0 and A=methyl, to give4-(6′-methoxy-2′-naphthyl)-2-butanone (Nabumetone™), which is animportant medicinal product.

A typical example of another α,β-unsaturated carbonyl compound ofgeneral formula (I) in which the C═C double bond is selectivelyhydrogenated according to the present invention is that in which Ar is(2′,3′-dimethoxyphenyl), n=0 and A is COOH, COO(C₁–C₄)alkyl orCOO-benzyl.

The following non-limiting examples serve to illustrate the presentinvention.

EXAMPLE 1

Preparation of Rh(TOA)/Al₂O₃

42 g of γ-alumina, 200 mg of RhCl₃. xH₂O (43.5% Rh), 140 ml of THF and1.44 ml of trioctylamine (TOA) were loaded, in the above order, at 25°C., into a 0.6 l glass reactor equipped with a mechanical stirrer, athermometer and a manometer.

The mixture was placed under stirring. 3 cycles of argon-vacuum and 2cycles of H₂-vacuum were performed. Next, the mixture was placed underpressure with hydrogen up to 0.5 atm (7.35 psi). After stirring for 24hours under H₂, the reaction was stopped.

The atmosphere was made inert by performing three cycles of Ar-vacuum.The reaction mixture was then filtered on a Buchner funnel.

The solid was washed with 140 ml of THF and then with 140 ml of H₂O.Finally, the solid was pressed and unloaded.

55 g (K.F. 29.6%) of Rh(TOA)/Al₂O₃ with a rhodium content equal to 0.12%were thus obtained.

EXAMPLE 2 Preparation of Rh(TOA)/Al₂O₃

105 g of γ-alumina, 500 mg of RhCl₃. xH₂O (43.5% Rh), 350 ml of THF and3.6 ml of TOA were loaded, in the above order, at 25° C., into a 1 lglass reactor equipped with a mechanical stirrer, a thermometer and amanometer.

The mixture was placed under stirring. 3 cycles of argon-vacuum and 2cycles of H₂-vacuum were performed. The mixture was then placed underpressure with hydrogen up to 0.5 atm (7.35 psi). After stirring for 24hours under H₂, the reaction was stopped.

The atmosphere was made inert by performing three cycles of Ar-vacuum.The reaction mixture was then filtered through a Buchner funnel.

The solid was washed with 100 ml of THF and then with 100 ml of H₂O.Finally, the solid was dried under reduced pressure.

100 g (K.F. ca. 3%) of Rh(TOA)/Al₂O₃ with a rhodium content equal to0.16% were thus obtained.

EXAMPLE 3 Preparation of Rh(TOA)/Al₂O₃

42 kg of γ-alumina, 0.2 kg of RhCl₃. xH₂O (43.5% Rh), 124 kg of THF and1.17 kg of TOA were loaded, in the above order, at 25° C., into a 200 lHastelloy reactor.

The mixture was placed under stirring. 3 cycles of nitrogen-vacuum and 2cycles of H₂-vacuum were performed. The mixture was then placed underpressure with hydrogen up to 0.5 atm (7.35 psi). After stirring at25–30° C. for 24 hours under H₂, the reaction was stopped.

The atmosphere was made inert by performing three cycles ofnitrogen-vacuum. The reaction mixture was then filtered through aBuchner funnel.

The solid was washed with 2×62 kg of THF, 3×40 l of H₂O and then driedfor 1 hour under reduced pressure (50 mmHg) at 50° C.

40 kg (K.F. 3.3%) of Rh(TOA)/Al₂O₃ with a rhodium content equal to 0.16%were thus obtained.

EXAMPLE 4 Preparation of Rh(TOA)/Al₂O₃

100 mg of RhCl₃. xH₂O (43.5% Rh), 10 ml of THF and 0.72 ml of TOA wereloaded, at 25° C., into a 50 ml glass round-bottomed flask equipped witha magnetic stirrer and a thermometer.

The mixture was placed under stirring. 3 cycles of argon-vacuum and 2cycles of H₂-vacuum were performed. The mixture was then placed under ahydrogen atmosphere for 24 hours.

The solution thus obtained was transferred into another round-bottomedflask containing a suspension of 20 g of γ-alumina in 35 ml of THF. Themixture was stirred for 6 hours under an H₂ atmosphere. The atmospherewas then made inert by means of three cycles of Ar-vacuum.

The reaction mixture was filtered through a Buchner funnel and the solidwas washed with 20 ml of THF and then with 2×10 ml of hexane.

After drying under reduced pressure, 20 g of anhydrous Rh(TOA)/Al₂O₃with a rhodium content equal to 0.15% were obtained.

EXAMPLE 5 Preparation of 4-(6′-methoxy-2′-naphthyl)-2-butanone

14.9 g of the compound of general formula (I) in whichAr=(6′-methoxy-2′-naphthyl), n=0 and A=methyl, and 1.42 g of wetcatalyst, prepared according to Example 1, in 100 ml of toluene wereplaced in a 250 ml autoclave.

Working at 75° C. and under 5 atm (73.45 psi) of hydrogen, theconversion was complete after 2.5 hours, with a selectivity towardsNabumetone of 98.7% and a TOF of ca. 1.6×10₃ h⁻¹.

At the end of the reaction, the mixture was filtered and the catalystwas reused in unmodified form on a fresh amount of compound (I), withidentical results in terms of kinetics and selectivity.

After recycling a further 3 times, the reaction was complete after 4.5hours with a selectivity>99% and a TOF of ca. 0.9×10³ h⁻¹.

EXAMPLE 6 Preparation of 4-(6′-methoxy-2′-naphthyl)-2-butanone

14.9 g of the compound of general formula (I) in whichAr=(6′-methoxy-2′-naphthyl), n=0 and A=methyl, and 0.95 g ofsubstantially anhydrous catalyst, prepared according to Example 2, in100 ml of toluene were placed in a 250 ml autoclave. The suspension wasstirred at 50° C. and under 5 atm (73.45 psi) of hydrogen. After 3.5hours, the conversion was complete, with a selectivity towardsNabumetone of 99% and a TOF of ca. 1.3×10³ h⁻¹.

EXAMPLE 7 Preparation of 4-(6′-methoxy-2′-naphthyl)-2-butanone

Working as in Example 6, but at 75° C. and under 15 atm (220.35 psi) ofhydrogen, the conversion was complete after 1.5 hours, with aselectivity towards Nabumetone of 98.7% and a TOF of ca. 3×10³ h⁻¹.

EXAMPLE 8 Preparation of 4-(6′-methoxy-2′-naphthyl)-2-butanone

10 g of the compound of general formula (I) in whichAr=(6′-methoxy-2′-naphthyl), n=0 and A=methyl, and 1.42 g of wetcatalyst, prepared according to Example 1, in 70 ml of toluene wereplaced in a 250 ml autoclave. The suspension was stirred at 50° C. andunder 5 atm (73.45 psi) of hydrogen. After 4.5 hours, the conversion wascomplete, with a selectivity towards Nabumetone of 98.5% and a TOF ofca. 0.6×10³ h⁻¹.

EXAMPLE 9 Preparation of 4-(6′-methoxy-2′-naphthyl)-2-butanone

1.18 kg of catalyst prepared according to Example 3 and a toluenesolution (130 l) containing 23.6 kg of the compound of general formula(I) in which Ar=(6′-methoxy-2′-naphthyl), n=0 and A=methyl, were loaded,in the above order, at 25° C., into a 200 l Hastelloy reactor.

The mixture was placed under stirring (200 rpm) and 3 cycles ofnitrogen-vacuum and 2 cycles of H₂-vacuum were performed. The reactionmixture was then heated to 50° C. and placed under pressure withhydrogen up to 15 atm (220.35 psi).

After 4.5 hours, the conversion was complete, with a selectivity towardsNabumetone of 98.7% and a TOF of ca. 1.3×10³ h⁻¹

COMPARATIVE EXAMPLE 1 Preparation of4-(6′-methoxy-2′-naphthyl)-2-butanone

Working as in Example 6, but using 0.075 g of a commercial anhydrous 5%Rh/Al₂O₃ catalyst or 0.15 g of a commercial 5% Rh/C catalyst with awater content of about 50% (with a precious metal content about 2–2.5times higher than that of the present invention) and under identicaltemperature and pressure conditions, the conversion was <50%.

With the abovementioned commercial catalysts, the conversion was 97–98%only after 6 hours at 20 atm (293.8 psi) and 70° C. However, theselectivity was less than 98% and the TOF was less than 3×10² h⁻¹.

COMPARATIVE EXAMPLE 2 Preparation of4-(6′-methoxy-2′-naphthyl)-2-butanone

4 g of the compound of general formula (I) in whichAr=(6′-methoxy-2′-naphthyl), n=0 and A=methyl, and 0.02 g of acommercial anhydrous 5% Rh/Al₂O₃ catalyst (with a precious metal contentabout 2.5 times higher than that of the present invention) in 150 ml ofethanol, were placed in a 250 ml autoclave.

After 6 hours at 20 atm (293.8 psi) and at 70° C., the conversion wasless than 95% and the selectivity less than 96%.

1. Process for preparing an Rh-based catalytic system heterogenized onan organic or mineral support, characterized in that: (a) a rhodiumderivative with a valency state >0 is reduced in an ether or aromaticsolvent and in the presence of a compound chosen from the groupconsisting of lipophilic tertiary amines, lipophilic tertiary amides andlipophilic quaternary ammonium salts, resulting in a mixture and (b) themixture is adsorbed onto a suitable organic or mineral support; whereinthe reduction is carried out by hydrogen transfer from a suitablehydrogen donor at a pressure of between 1 and 5 atm (14.69–73.45 psi)and at a temperature of between 15 and 40° C.
 2. Process according toclaim 1, wherein the rhodium derivative is a halide.
 3. Processaccording to claim 2, wherein the ether or aromatic solvent is chosenfrom the group consisting of tetrahydrofuran, 1,2-dimethoxyethane,diglyme, toluene, mesitylene, isopropylbenzene and cumene.
 4. Processaccording to claim 3, wherein the lipophilic tertiary amine is an amineof formula NTT′T″, in which T, T′ and T″, which may be identical ordifferent, are a linear or branched alkyl containing from 4 to 20 carbonatoms, a cycloalkyl containing from 5 to 10 carbon atoms or analkylphenyl in which the alkyl contains from 1 to 20 carbon atoms. 5.Process according to claim 3, wherein the lipophilic tertiary amide isan amide X—CO—NX′X″, in which X′ and X″, which may be identical ordifferent, are a linear or branched alkyl containing from 4 to 20 carbonatoms, a cycloalkyl containing from 5 to 10 carbon atoms or analkylphenyl in which the alkyl contains from 1 to 20 carbon atoms. 6.Process according to claim 3, wherein the lipophilic quaternary ammoniumsalt is a quaternary salt of formula [NY¹Y2Y³Y⁴]⁺ Z⁻ in which Y¹, Y², Y³and Y⁴, which may be identical or different, are a linear or branchedalkyl containing from 1 to 20 carbon atoms, a cycloalkyl containing from5 to 10 carbon atoms or an alkylphenyl in which the alkyl contains from1 to 20 carbon atoms, on condition that the total number of carbon atomsin the quaternary salt is at least 14; Z⁻ is Br⁻, Cl⁻, OH⁻ or HSO₄. 7.Process according to claim 4, wherein the tertiary amine trioctylamineor hexadecylamine.
 8. Process according to claim 4, wherein the (amineor amide or ammonium salt)/rhodium salt molar ratio is between 2 and 5.9. Process according to claim 8, wherein the mineral support is chosenfrom the group consisting of: Al₂O₃, pumice, hydrotalcite, C, SiO₂zeolites, TiO₂ and ZrO₂.
 10. Process according to claim 9, wherein themineral support is a γ alumina.
 11. Process according to claim 10,wherein the catalytic system is prepared in a single phase.
 12. Processaccording to claim 1, wherein the ether or aromatic solvent is chosenfrom the group consisting of tetrahydrofuran, 1,2-dimethoxyethane,diglyme, toluene, mesitylene, isopropylbenzene and cumene.
 13. Processaccording to claim 1, wherein the (amine or amide or ammoniumsalt)/rhodium salt molar ratio is between 2 and
 5. 14. Process accordingto claim 1, wherein the mineral support is chosen from the groupcomprising: Al₂O₃, pumice, hydrotalcite, C, SiO₂ zeolites, TiO₂, andZrO₂.
 15. Process according to Claim 1, wherein the catalytic system isprepared in a single phase.
 16. Process according to claim 1, whereinthe reduction is carried out with hydrogen.
 17. Process forhydrogenating the C═C double bond in α,β-unsaturated carbonyl compoundsof general formula (I) according to the following reaction scheme:

in which A is hydrogen, linear or branched alkyl containing from 1 to 8carbon atoms, cycloalkyl containing from 5 to 10 carbon atoms, COOR orCONRR′ in which R and R′, which may be identical or different, arehydrogen, linear or branched alkyl containing from 1 to 8 carbon atomsor cycloalkyl containing from 5 to 10 carbon atoms, or A has themeanings given below for Ar n is 0, 1 or 2; Ar is phenyl, naphthyl or a5- to 7-membered heteroaryl containing 1 or 2 hetero atoms chosen fromO, N and S, in which the said phenyl, naphthyl and heteroaryl may besubstituted with one or more C₁–C₂ alkyl groups or one or more OH, OR,halogen, COOR or CONRR′ groups, in which R and R′, which may beidentical or different, are hydrogen, benzyl, linear or branched alkylcontaining from 1 to 8 carbon atoms or cycloalkyl containing from 5 to10 carbon atoms, wherein the hydrogenation is carried out by contactingα,β-unsaturated carbonyl compounds with an Rh-based catalytic systemprepared according to claim
 4. 18. Process according to claim 17,wherein the hydrogenation is carried out at a temperature of between 0°and 100° C.
 19. Process according to claim 18, wherein the hydrogenationis carried out at a temperature of between 20° and 80° C.
 20. Processaccording to claim 19, wherein the hydrogenation is carried out at apressure of between 1 (14.69 psi) and 20 atm (293.8 psi).
 21. Processaccording to claim 20, wherein the hydrogenation is carried out in thepresence of a solvent of medium or low polarity chosen from the groupcomprising linear or branched aliphatic hydrocarbons containing from 6to 12 carbon atoms; cyclic hydrocarbons containing from 6 to 10 carbonatoms; aromatic hydrocarbons: aliphatic esters; aliphatic ethers andchlorinated aliphatic solvents.
 22. Process according to claim 21,wherein the solvent of medium or low polarity is chosen from the groupcomprising toluene, xylene, mesitylene, isopropylbenzene, cumene, ethylacetate, isopropyl acetate, butyl acetate, tetrahydrofuran andmesitylene chloride.
 23. Process according to claim 22, wherein in thecompound of general formula (I), Ar is (6′-methoxy-2′-naphthyl) or(2′,3′-dimethoxyphenyl), n=0 and A is methyl, COOH, COOO(C₁–C₄)alkyl orCOO-benzyl.
 24. Process according to claim 17, wherein the hydrogenationis carried out at a pressure of between 1 (14.69 psi) and 20 aim (293.8psi).
 25. Process according to claim 17, wherein the hydrogenation iscarried out in the presence of a solvent of medium or low polaritychosen from the group comprising linear or branched aliphatichydrocarbons containing from 6 to 12 carbon atoms; cyclic hydrocarbonscontaining from to 10 carbon atoms; aromatic hydrocarbons: aliphaticesters; aliphatic ethers and chlorinated aliphatic solvents.
 26. Processaccording to claim 17, characterized that, wherein in the compound ofgeneral formula (I), Ar is (6′-methoxy-2′-naphthyl) or(2′,3′-dimethoxyphenyl), n=0 and A is methyl, COOH, COOO(C1–C4)alkyl orCOO-benzyl.